Gestational sac

Gestational sac

Infobox Embryology
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The gestational sac (or gestation sac) is the only available intrauterine structure that can be used to determine if an intrauterine pregnancy (IUP) exists, until the embryo is identified.

On ultrasound, it is an anechoic (dark) space surrounded by a hyperchoic (white) rim.

It is spherical in shape, and usually located in the upper uterine fundus.

The mean gestational sac diameter (MGD) is an effective estimate of gestational agecite journal |author=Karki DB, Sharmqa UK, Rauniyar RK |title=Study of accuracy of commonly used fetal parameters for estimation of gestational age |journal=JNMA; journal of the Nepal Medical Association |volume=45 |issue=162 |pages=233–7 |year=2006 |pmid=17189967 |doi=] between 5 and 6 weeks, with an accuracy of about +/- 5 days. [cite web |url=http://radiology.creighton.edu/pregnancy.htm |title=Basic Imaging > Ultrasound of Early Pregnancy |accessdate=2007-10-13 |format= |work=]

The yolk sac and embryo should be readily identified when the gestational sac reaches a certain size and the yolk sac is 20 mm in size or the fetal pole is 25 mm in size.

Characteristics on ultrasound

Gestational sacs can be identified via ultrasound and are generally identified by the following 4 characteristics: 1. Round or elliptical shape in longitudinal and transverse views2. Surrounded by an echogenic rim (choriodecidual reaction)3. Gestational sac is in uterine fundus4. Sac is not directly midline, but implanted eccentrically (to one side of the uterine cavity line, without displacing it).

References


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